The present invention relates to improvements in bead lock means for a tire-forming drum of a second-stage apparatus for use in a tire-forming method of the second-stage type in the manufacture of radial tires.
In the manufacture of such radial tires, a tire-forming method of the second-stage type has heretofore been adopted extensively. According to this method, after a cylindrical green case has been formed by an apparatus of the first stage, it is conveyed to an apparatus of the second stage where the green case is arranged at said apparatus and formed in a toroidal shape and further, a belt and a tread are incorporated therein so as to complete a green tire.
Various types of such tire-forming drum of said second-stage apparatus have been proposed up to now, for example, there are such types as are disclosed in Japanese Patent Publications Nos. 5349/1978, 6266/1979 and 32544/1980.
So far as these types are concerned, all of them show a portion for the mounting of a cylindrical green case (so-called former ring) in the form of a cylindrical and integral body having a diameter larger than the internal diameter of the bead portion of the green case to be received thereby.
Therefore, in the case of mounting the green case preformed by an apparatus of the first stage on a drum of apparatus of the second stage, it becomes necessary to incline the green case in order to mount it over the flange of the drum which has a large diameter, to transform the shape of the bead portion once and for a while, or to remove one side of said flange temporarily. These operations cannot be carried out but by manual handling and this has become the cost factor for plant operation and has lowered the productivity.
On the other hand, as means for eliminating such inconvenience, for example, Japanese Patent Publication No. 37720/1975 discloses one type wherein the ring opposite to the headstock is capable of expanding and contracting.
However, when transforming the green case into a toroidal shape in cases where the tire shows the tendency of allowing the bead portion to be slipped inwardly from the viewpoint of the properties of structure of the tire to be transformed, it becomes necessary to provide a slip-regulating portion of a diameter larger than the internal diameter of the green case also inwardly of the aforesaid ring for the purpose of regulating such a slip of the tire and therefore, no sufficient effect can be expected thereof.
Also, it is considered that the ring at the headstock side (hereinafter called right-side) may be made expansive and contractive in the same manner as that of the side opposite to the headstock (hereinafter called left-side) but in such a case, there occurs the need for the provision of many pipes for supplying pressure air as a driving source for expansion and contraction of the ring. Specifically, the right-side requires two pipes, i.e., one for expansion and the other for contraction and two similar pipes for communication from the left-side to the right-side (pressure air may be supplied to the right-side from the right direction but it requires four pipes in all from the source of supply). Thus, at least two pipes will be necessary from the source of supply to the drum and according to this system of piping arrangements, the pipes are caused to pass inside the shaft in general and therefore, besides the aforesaid two pipes inside the shaft, one pipe for the supply of pressure air must be added for the purpose of making the tire into a toroidal shape, thus amounting to three pipes in all as a piping system. If so, the provision of three independent pipes inside the slender and long shaft is sure to result in increased cost of manufacture.
Moreover, even if the diameter of bead portion of a green case to be received is the same throughout, there are frequently differences in the holding diameter of the bead portion, depending on differences of tire size. For example, if the so-called diameter of a bead portion is 20", there are differences in the internal diameter of the bead portion of the green case depending on the difference in thickness for use in 10.00R20, 11.00R20 and 12.00R20 of different sizes and also depending on the difference in number (number of layers) of parts to be incorporated therein. Accordingly, in the case of providing an economical drum, namely in the case of forming several kinds of green cases of somewhat different diameters by the use of a single drum, delicate adjustment of the aforesaid drum cannot be performed satisfactorily at the time of expansion in diameter, and it is not only necessary to prepare a different drum per green cases of different diameter but also the productivity tends to be lowered on account of the replacement of the drum.